| With the large consumption of fossil fuels,the issue of environmental pollution arises in our society.Novel discoveries in materials science have been pursued by researchers to overcome the obstacle for effective energy conversion.Semiconductor-based photocatalysis,in which the clean solar energy can be harvested and transformed into hydrogen as a feasible technology,have gained considerable attention.Silicon carbide(SiC)is a significant inorganic semiconductor material due to its hardness,low cost and environmental friendliness.More importantly,it can absorb the visible light and the conduction band lies above the reduction potential of H+ to H2.In this consideration,SiC is prone to be a valuable material as a photocatalyst for water splitting.In this thesis,the photocatalytic ability of SiC-based materials under visible light has been systematically investigated.Through hybridizing caldium sulfide(CdS)on the surface of SiC,an effective Z-scheme was constructed to shuttle charge-carriers.Afterwards,the heterogeneous interface was further optimized by hydrothermal synthesis.The effect of lattice match to the growth of heterojunction was explored as well.In addition,the orgainic coupling agent was introduced to the composite and applied as the bridge to transfer the electrons and holes.The detailed results are summarized as follows:(1)The deposition of CdS on SiC was achieved by wet synthesis.The low surface activiation energy spots had been reported and the direct Z-scheme was successfully constructed to shuttle charge carriers.Photocatalytic activity of SiC was significantly enhanced to 555 ?mol·h-I·g-1,a value even much higher than that of CdS.The PHE activity can be further increased up to 5460 ?mol-h-1·g-1 if 3 wt%Pt was added.The apparent quantum efficiency(AQE)reaches 2.1%at 420 nm.The self-corrosion of CdS was simultaneously avoided and the composites showed high stability.(2)The content of CdS was tuned by theoretical calculation and the dispersion homogeneity of hexagonal CdS nucleated on hexagonal SiC surface was controlled by a hydrothermal method.The heterogeneous structure on the catalyst interfaces was achieved.Meanwhile,the strong light-absorption,large BET surface area and prolonging carrier-lifetime were also obtained in the well-contacted composite.These results contributed to a doubly-enhanced photocatalytic performance under visible light.(3)The effect of lattice match between SiC and CdS had been investigated by constructing different lattice hybridization.Two structures of CdS were obtained by altering the hydrothermal temperature.The H-220 sample with H-CdS/H-SiC crystal type demonstrated a fourfold improvement in photocatalytic activity compared to the mismatched sample with C-CdS/H-SiC,and reached 259?mol·h-1·g-1.Lattice match is thought to be achieved between two hexagonal compounds with a lattice constant relationship of 3aH-cds=4aH-sic,and it plays an important role in forming efficient heterojunctions to enhance the photocatalytic performance.(4)The organic silane coupling agent,(3-Mercaptopropyl)trimethoxysilane(MPTMS),was introduced into the inorganic SiC/CdS photocatalytic system as a bridge to transfer the photo-generated electrons.The Si-O-Si bond was developed between MPTMS and SiC and prolonged the lifetime of charge-carriers.The photocatalytic hydrogen evolution ability had triple improved than the one without MPTMS.It suggests that MPTMS can effectively improve water splitting ability and will be helpful in designing new composite photocatalytic systems. |
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